Hillary Clinton’s presidential campaign was thrown into turmoil by the leak of emails documenting dirty tactics by the Democratic party leadership. Suggestion of attempts to rig the primary contest in her favour is not merely embarrassing; it is bound to anger supporters of her defeated rival, Bernie Sanders, and deepen the party’s divisions. But this should not be a source of satisfaction for Republicans. They should be equally alarmed by the possibility that the leak came from Moscow — marking a serious escalation in the long term trend of Russian aggression in cyber space.

It is extremely difficult to pin down the source of a hacking attack — especially given the Kremlin’s tendency to outsource such work to criminal groups or pro-government organisations. However, cyber security firms have set out credible evidence to identify the groups responsible for hacking the Democratic National Committee’s network — best known as APT 28 and APT 29. They say that the techniques these groups use, the timezone in which they operate and their previous targets — including the White House and US State Department, eastern European governments and Nato — suggest close links to the Kremlin or Russian security services.

It would hardly be a new development for Moscow to adopt such tactics. As far back as 2007, Estonia suffered crippling attacks on the websites of its banks, government and telecoms networks. Georgian state websites were targeted shortly before the outbreak of war in 2008. Of course, many other governments, the US foremost among them, employ similar methods to gather intelligence and counter security threats.